Transcriptomic analysis reveals overdominance playing a critical role in nicotine heterosis in Nicotiana tabacum L.

As a unique biological phenomenon, heterosis has been concerned with the superior performance of the heterosis than either parents. Despite several F1 hybrids, containing supernal nicotine content, had been discovered and applied to heterosis utilization in Nicotiana tabacum L., nevertheless, the potential molecular mechanism revealing nicotine heterosis has not been illustrated clearly. Phenotypically, the F1 hybrids (Vall6 × Basma) show prominent heterosis in nicotine content by 3 years of field experiments. Transcriptome analysis revealed that genes participating in nicotine anabolism (ADC, PMT, MPO, QPT, AO, QS, QPT, A622, BBLs) and nicotine transport (JAT2, MATE1 and 2, NUP1 and 2) showed an upregulated expression in the hybrid, a majority of which demonstrated an overdominant performance. RT-PCR confirmed that nicotine anabolism was induced in the hybrid. These findings strongly suggest that nicotine synthesis and transport efficiency improved in hybrid and overdominance at gene-expression level played a critical role in heterosis of nicotine metabolism.